The clinical utility of imaging techniques to evaluate suspected traumatic injury to the cranio-cervical junction (CCJ) continues to be debated in recent literature. Findings from this study add to the body of literature examining the use of dynamic radiographs to evaluate segmental stability of the cervical spine.
To our knowledge, the inter-rater reliability of AP-OM lateral bending radiograph interpretation has not been previously assessed in any population. The technique requires precise patient positioning to ensure accuracy and minimize the degree to which overlapping structures interfere with interpretation. These technical considerations introduce potential variability in interpreting these images, their associated measurements, and their clinical significance. AP-OM dynamic lateral bending radiographs may represent an additional tool in evaluating atlantoaxial hypermobility, visualizing increased atlantoaxial movement under end-range stress conditions [14, 20, 21] Some studies have proposed that such radiographic findings may be associated with pathology, one of which was performed in a population of patients with refractory symptoms after mild traumatic brain injury . Increased motion may be visualized if alar ligament laxity is present – seen as an ipsilateral “offset” adjacent to the lateral C1-C2 joint and corresponding inset of the contralateral side with minimal C2 spinous rotation. Additionally, a step off of greater than 1–2 mm at the lateral margin of the lateral C1-C2 joint during ipsilateral bending has been proposed as an indicator of significant hypermobility of the CCJ, although the validity of this measurement has not been investigated.
One previous study examined the use AP-OM lateral bending radiographs to characterize CCJ hypermobility in a cohort of patients diagnosed with rheumatoid arthritis . They used measurements to calculate the amount of atlanto-dental lateral shift (ADLS), ostensibly indicating lateral hypermobility of the C1–2 joint (RA); the data within the RA cohort was compared with healthy controls. They reported that excessive motion of the C1–2 joint on lateral bending radiographs – quantified by the magnitude of ADLS – was just as prevalent as anterior C1–2 hypermobility noted on forward flexion radiographs. The authors concluded the ADLS measurement was sensitive to early atlantoaxial disease in patients who did not yet demonstrate findings in traditional lateral views with flexion, suggesting that AP-OM radiographs are more sensitive to a lesser amount of segmental motion. One follow-up study described a variant on this technique, evaluating ADLS using close-mouth lateral bending views . The technique, while potentially useful, has not yet been evaluated comparing normative data with diseased populations. These findings suggest that AP-OM dynamic views may provide a useful imaging technique, which complements the use of CT and MRI in evaluation of CCJ injury.
One seemingly paradoxical finding was the low Kappa values for normal spinous movement compared with the high raw percentage of overall agreement; this is particularly apparent in the complete inability to compute a kappa value for normal spinous movement left. This paradox relates to the fact that calculation of the kappa statistic is highly sensitive to the prevalence of the observed clinical finding. In our 56 cases, the vast majority of images showed normal C2 spinous movement to opposite side of lateral bending, which may artificially inflate the raw percentage of agreement and confound calculation of the kappa statistic due to the high prevalence of this finding.
There are conflicting reports on the utility of the odontoid lateral mass interspace (OLMI) in predicting occult injury, as measured both on cross sectional imaging and radiographs. It has been shown that static CT imaging often reveals OLMI asymmetry in asymptomatic patients . One recent study found that OLMI as measured on static CT imaging lacks sensitivity and specificity in detecting ligamentous injury, unless optimal technique is employed . When measured on odontoid open-mouth radiographs, OLMI asymmetry may be an indicator of serious occult injury such as rotary subluxation or fracture . Several studies have suggested, however, that OLMI may demonstrate asymmetry of 2 mm or greater in the absence of any pathology [25, 28, 29].
The clinical utility of MRI in evaluating CCJ is questionable and somewhat controversial. Isolated case studies have revealed mixed results in evaluating abnormal signal intensity within the alar and transverse ligaments on fast spin-echo (FSE) T2 and proton density (PD) sequences [6, 8, 9, 30]. Follow-up studies evaluating MRI in Whiplash Associated Disorders (WAD) and other clinically relevant but non-traumatic diagnoses such as chronic neck pain, cervicogenic headache, and migraine headaches have not confirmed any significant correlation with trauma, either acutely or remotely [10, 31, 32]. The majority of these studies evaluated ligamentous injury using a four-point grading scale.
Many authors have noted concerns regarding the use of MRI in evaluating occult CCJ injury. Given the above noted small study sizes, a more recent meta-analysis attempted to evaluate these data using stronger statistical methods . The authors concluded that abnormal imaging findings did not correlate with symptoms and that there was no evidence to support the assertion that MRI reveals ligamentous injury in this patient population. Several studies have revealed issues with the reliability of image interpretation, as well as technical difficulties with patient positioning and image acquisition when performing these sequences [8, 9, 11,12,13, 33]. Lastly, this imaging technique may be inaccurate unless optimal technique is employed, necessitating expertise by involved staff [11, 13, 26]. These conflicting data highlight the need to investigate complementary imaging techniques which may reveal occult CCJ injury; additional methods of dynamic radiography, as described in this study, may provide that complement. The need for effective and reliable evaluative techniques is underscored by the growing recognition of upper cervical spine injury as a potential underlying factor in the persistent symptoms after concussion injury . Many athletes who sustain a concussion often injure both their neck and head. Among cervical spine injuries, the upper cervical spine has the greatest anatomic connection and neurologic cross-innervation with head [20, 34]. It follows that, in these patients who suffer prolonged headache and dizziness, occult injury of the CCJ complex may be more common than currently suspected and may frequently go unrecognized. It is also important to note that occult traumatic injury to the CCJ has been shown to be more frequent in the pediatric population [35, 36] where concussions are more frequent and symptoms are persistent. Thus, it is imperative that we continue to develop imaging techniques for the cervical spine which complement currently available technology, minimize radiation, and constrain costs when appropriate.